Non-destructive monitoring of moisture at the steel-concrete interface with embedded RFID MEMS sensors
File(s)
Author(s)
Liew, Jia
Type
Thesis
Abstract
The moisture state of concrete and entrapped air voids at the steel-concrete interface are important influences on the corrosion of reinforced concrete, but the detail of these relationships is unclear. This study investigates the suitability of monitoring relative humidity at the steel-concrete interface with radio-frequency identification (RFID) microelectromechanical systems (MEMS) sensors in customized polylactic acid enclosures. This involved prototyping and calibrating enclosure designs, determining the influence of cementitious material on wireless communication and embedding RFID MEMS sensors in concrete specimens. It was shown for the first time that relative humidity at the steel-concrete interface can be monitored for samples with different curing ages, nominal cover depths and water to cement ratio, demonstrating the suitability of such a device for laboratory-based research.
The method was used to monitor relative humidity changes in air voids in specimens subjected to wetting and drying. The effects of sample preparation, void size and microcracks at the paste-void interface (characterised by SEM-BSE) induced by drying conditions were also examined. It was shown that RFID MEMS sensors were capable of monitoring relative humidity changes in air voids with faster rates of saturation for smaller voids compared to larger voids.
The durability and reliability of sensor components were also investigated. RFID MEMS sensors were subjected to 1 year of cyclic wetting and drying, 7 months of embedment in high and low-strength concrete, 3 months of exposure to 3% wt. NaCl salt solution and 100% RH environment. The impact of cementitious material on sensor components was studied with SEM-BSE and EDS. Surface morphology of MEMS sensors was also examined and related to relative humidity measurements to explain changes in performance. Results demonstrated that similar measurements were obtained when compared to unexposed sensors; however, performance was affected after exposure to 3% wt. NaCl salt solutions for 63 days.
The method was used to monitor relative humidity changes in air voids in specimens subjected to wetting and drying. The effects of sample preparation, void size and microcracks at the paste-void interface (characterised by SEM-BSE) induced by drying conditions were also examined. It was shown that RFID MEMS sensors were capable of monitoring relative humidity changes in air voids with faster rates of saturation for smaller voids compared to larger voids.
The durability and reliability of sensor components were also investigated. RFID MEMS sensors were subjected to 1 year of cyclic wetting and drying, 7 months of embedment in high and low-strength concrete, 3 months of exposure to 3% wt. NaCl salt solution and 100% RH environment. The impact of cementitious material on sensor components was studied with SEM-BSE and EDS. Surface morphology of MEMS sensors was also examined and related to relative humidity measurements to explain changes in performance. Results demonstrated that similar measurements were obtained when compared to unexposed sensors; however, performance was affected after exposure to 3% wt. NaCl salt solutions for 63 days.
Version
Open Access
Date Issued
2023-03-16
Date Awarded
01/10/2023
Advisor
Buenfeld, Nick
Wong, Hong S.
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)